The present invention relates to a method for forming a monolayer powder film by embedding powders in an adhesive layer consisting of acrylic type adhesive previously formed on the surface of a base material, so that part of the powder is exposed. Additionally, the present invention relates to a production method for a filler lens which is suitable for use in displays such as LCDs, ELs, FEDs, etc., and which in particular, yields superior effects in which nonuniformity of luminance in these displays is avoided and contrast therein is improved.
As a general conventional method in which powders are adhered to a base material, (1) flowing and soaking methods in which powders are sprayed on a base material preheated to above the melting point of the powder and are adhered by melting; (2) electrostatic spray method in which powders are charged and sprayed on a base material by air spraying; (3) electrostatic flowing and soaking method in which a base material is soaked in a powder coating material fluidized by charged air and powders are adhered to the base material by electrostatic attraction; and (4) electrodeposition method in which charged powders are dispersed into solution and are supported on a base material by applying voltage; etc., can be used.
As a powder coating method proposed in Japanese Patent Application Publications, etc., (5) a method in which an adhesive layer consisting of uncured resin is previously formed on the surface of a base material, powder coating materials adhered to the surface of film forming media are embedded in the adhesive layer by using external force such as vibration, procedures in which powders are further embedded in the adhesive pushed out on the surface in the above embedding procedure by the film forming media are repeated, and then a powder film is completely formed at which pushing out of the adhesive is stopped, is disclosed in Japanese Unexamined Patent Publication No. 5-302176. In addition, (6) methods in which an adhesive layer is formed on a base material, transparent microspheres are placed on the adhesive layer, the surface thereof is leveled by skizing, and then the transparent microspheres are embedded in the adhesive layer by presses, pressure rollers, etc., are disclosed in Japanese Unexamined Patent Publications No. 9-318801 and No. 11-95004.
However, film forming methods of the above (1) to (4) are methods for adhering powders on the surface of a base material in multilayers, and the methods theoretically cannot form a monolayer powder film in which powders are uniformly filled in the planar direction at high density.
In contrast, according to the coating method (5), since uncured liquid resin is used as an adhesive layer, the adhesive oozes from spaces and is adhered to the powders and a powder adhered layer is formed as a multilayer. In addition, in this coating method, if the film forming media and the base material are not vibrated or stirred at the same time, the film forming media adhere to the surface of the adhesive layer. Therefore, it was unsuitable for coating base materials having a large area such as film or sheet materials.
Furthermore, in the coating method (6), filling density of the powders in the planar direction is often not uniform, and dense regions and sparse regions of the powders in filling density are easily formed. In addition, in this method, it was also difficult to embed the powders to a uniform depth in the adhesive layer. That is, pressure differences partially occur, depending on partial bending of pressure rollers or presses, dispersion of thicknesses in an adhesive layer, dispersion of thicknesses in a film, etc. At a place at which a large pressure is applied, an adhesive layer is easily formed as a multilayer because powders are deeply embedded, adhesive oozes from openings adhered to the powders, and other powders are adhered thereon. In contrast, at a place at which a slight pressure is applied, defects such as powder coming out easily occur in washing processes for surplus powder, etc., because powders have not been sufficiently embedded in the adhesive layer. This phenomenon is pronounced in the case in which a large area is coated or in the case in which the volume average particle diameter of powders to be used is 15 xcexcm or less. In particular, in the case in which the volume average particle diameter of powders to be used is 15 xcexcm or less, since the specific surface area of the powders is increased and the fluidity of the powders is substantially deteriorated by effects of interparticle forces such as van der Waals forces, electrostatic attraction such as frictional electrostatic charging, etc., it was difficult for powders to be adhered uniformly to the surface of the adhesive layer at high densities. Furthermore, if powders in which volume average particle diameter is 15 xcexcm or less are used, since the pressure from pressure rollers disperses and the pressure applied to each powder is lowered, other powders cannot be embedded to uniform depth in spaces between the powder particles already adhered on the adhesive layer. Therefore, the filling density of the powders is low, and dispersion of embedding depths of the powders in the adhesive layer is also increased by the above partial dispersion of pressure.
Additionally, there has been remarkable progress in displays such as LCDs, ELs, FEDs, etc., recently. In particular, the LCD has spread through numerous fields such as notebook-size personal computers, portable type terminals, etc., and this is anticipated to continue in the future. LCDs may be divided into reflecting types and transmitting types, depending on the manner in which illuminating light is taken into the liquid crystal panel. The reflecting type uses a method in which a reflecting plate on which an aluminum film, etc., is adhered having a high reflectivity is arranged in the back of a liquid crystal panel; external light transmitted from a surface side of the display is reflected by the reflecting plate; the liquid crystal panel is illuminated; and a liquid crystal image is obtained. In contrast, the transmitting type uses a method in which a liquid crystal panel is illuminated by a back light unit arranged in the back of the liquid crystal panel. In the reflecting type, in order to prevent loss of contrast in which the native color of the aluminum appears, the background color is made to closely resemble paper white color by inserting a medium which moderately diffuses the light between the liquid crystal panel and the reflecting plate. In addition, the back light unit in the transmitting type is generally provided with a light source such as an acrylic light conducting board having a cold cathode tube and a light diffusing board diffusing light from the light source, and is a composition in which uniform planar light illuminates the liquid crystal panel.
Thus, in either of the methods used in the reflecting type and transmitting type, a medium having a light diffusivity (hereinafter referred to as xe2x80x9clight diffusion materialxe2x80x9d) is used. As this light diffusion material, for example, a material in which adhesive resin dispersed fillers having light diffusivity is laminated on one surface of a transparent resin film, can be employed. Such conventional light diffusion materials have been produced by a method in which a coating material is prepared by dispersing fillers in a solution dissolved solvent in adhesive resin, and this coating material is coated on a film by a spray or a coater. In FIG. 17, a light diffusion material obtained by such a production method is schematically shown, and an adhesive layer 22 is formed on a film 21 by curing adhesive resin solution and fillers 23 are dispersed in this adhesive layer 22.
With respect to total light diffusion transmittance and total light diffusion reflectance in the above conventional light diffusion material, these values in a direction of incident light in which light is transmitted from a filler side are almost similar to these values in a direction from a film side, and these show equal values. It is found that light diffusivity is the same regardless of the incidence direction of the light, that is, there is no directivity. This is the reason that fillers are perfectly embedded in an adhesive layer, fillers overlap in a thickness direction, and a multilayer is thereby formed; the surface shape of the light diffusion material becomes a relatively symmetrical sine curve when filling density of fillers is coarse; etc.
Therefore, the inventors have conducted various research in order to produce a filler lens in which fillers are embedded so that part of the filler protrudes on the surface of an adhesive layer and in which protruding filler serves as a fine lens, and have developed a method for embedding fillers in an adhesive layer by striking to fillers using external force via pressure media, so that production of a filler lens which exhibits light diffusivity having a directivity was attained.
However, according to the above filler lens, since the adhesive of the adhesive layer maintains a condition having flexibility in the case of embedding fillers, the embedding condition of the fillers changed due to the thermal fluidity of the adhesive, in particular under high-temperatures and high-humidity, and it was difficult for reliable optical properties, that is, specific optical properties, to be maintained.
It is an object of the present invention to provide a coating method in which a monolayer powder film is uniformly formed on a base material, even if fine powders as described above are employed having a volume average particle diameter of 15 xcexcm or less with which it was difficult to produce films by conventional coating methods. A xe2x80x9cmonolayer powder filmxe2x80x9d according to the present invention refers to a film formed in order to give various functions such as polishing, non-slipping or slipping, light-reflecting or anti-reflecting, insulating or conducting, light condensing or diffusing using in a flat lens, a translucent screen, polarization element, etc., on a surface of a base materials, in addition to a general coating film for esthetic enhancement and for improving durability and strength of the surface.
A forming method for film according to the present invention is characterized by comprising a process for forming an adhesive layer consisting of an adhesive having a weight average molecular weight of 250,000 or more on a base material directly or via another layer, a process for adhering powders to a surface of the adhesive layer, a process for embedding the powders on a surface of the adhesive layer by granular pressure media and forming a powder layer as a monolayer, and a process for removing surplus powder adhering to a laminate formed above. Therefore, according to the present invention, each property of the powders can be imparted by coating a super thin film on the surface of a base material, and the method can be applied to various uses.
Additionally, it is an object of the present invention to provide a production method for a filler lens in which the lens effect of the filler is sufficient and the optical properties are maintained even under high-temperatures and high-humidity. A production method for a filler lens according to the present invention is a method for producing a filler lens comprising a base material, an adhesive layer provided on said base material directly or via another layer, consisting of at least radiation-curable resin, a filler layer in which fillers are embedded on a surface of the adhesive layer so that part of the filler protrudes from a surface thereof, and it is characterized by comprising a process for forming the adhesive layer on the base material directly or via another layer, a process for embedding the fillers on a surface of the adhesive layer by striking the filler using an external force via pressure media, a process for curing the adhesive layer, and a process for removing surplus powders adhered to a laminate formed above. As a method for embedding fillers in an adhesive layer, specifically, a method in which granular pressure media are vibrated, the pressure media strike fillers, and the fillers are thereby embedded in an adhesive layer, can be employed.
According to the production method for a filler lens of the present invention, a filler lens having a composition in which the embedding depths of fillers are made uniform, fillers are placed in the planar direction at high density, and fillers are embedded as a monolayer on a surface of the adhesive layer so that part of the filler protrudes from a surface thereof. Furthermore, in this filler lens, since the adhesive of the adhesive layer in which the fillers are embedded is cured, the adhesive will not flowed by heating even under high-temperatures and high-humidity, and optical properties of the filler lens can be thereby maintained constant.
The present invention consists of two kinds of compositions in the first embodiment which is a general forming method for monolayer powder film applied to various uses and the second embodiment applied to production of the filler lens. FIG. 1 is a sectional view schematically showing an example of a powder film or a filler lens obtained by a method according to the first embodiment or the second embodiment of the present invention. In this monolayer powder film (filler lens) L, an adhesive layer 2 is coated directly on a base material 1, a large number of powder particles (fillers) 3 are embedded as a monolayer on a surface of this adhesive layer 2 so that parts thereof protrude from a surface of the adhesive layer 2 and the fillers are placed in the planar direction at high density, and a powder layer (filler layer) 3A is thereby formed.
In the following, each embodiment will be explained in detail.
Firstly, a forming method for monolayer powder film according to a first embodiment of the present invention is explained in the order of the process.
Process 1: Coating Adhesive Layer
As a base material, film shaped materials or sheet shaped materials, in which an adhesive layer can be coated by a coater, are preferable. Specifically, various resin films consisting of polyethylene terephthalate (PET), polyethylene naphthalate (PEN), triacetyl cellulose (TAC), polyalate, polyimide, polyether, polycarbonate, polysulfone, polyethersulfone, cellophane, aromatic polyamide, polyethylene, polypropylene, polyvinyl alcohol, etc., can be suitably employed. In addition, as a base material other than such resin films, hard plates consisting of the above resin, sheet shaped members consisting of glass material such as silica glass, soda glass, etc., can be employed. Both transparent base materials and non-transparent base materials can be employed, and in particular, the thickness of the base material is preferably 1 xcexcm to 5 mm in consideration of productivity.
As a layer provided as necessary, a binding layer for firmly adhering an adhesive layer to a base material, coloring layer, conductive layer, charged layer, antistatic layer, adjusting layer for adjusting refractive index or transmittance of light, etc., can be appropriately employed according to application and purpose.
Furthermore, as an adhesive for forming an adhesive layer, adhesives consisting of resin such as polyester type resin, epoxy type resin, polyurethane type resin, silicone type resin, acrylic type resin, etc., can be employed. These may be employed alone or in combination. In particular, an acrylic type adhesive is preferred, since water resistance, heat-resistance, light resistance, etc., are superior, adhesive strength and transparency are good, and in addition, the refractive index is easily adjusted when the adhesive is used for an optical use. As an acrylic type adhesive, a homopolymer or copolymer of acrylic monomer such as acrylic acid and an ester thereof, methacrylic acid and an ester thereof, acrylamide, acrylic nitrile, etc., and a copolymer of at least one kind of the above acrylic monomers and aromatic vinyl monomer such as vinyl acetate, maleic anhydride, styrene, etc., can be employed. In particular, a copolymer consisting of a primary monomer for providing adhesiveness such as ethylene acrylate, butylacrylate, 2-ethylhexyl acrylate, etc., a monomer as a cohesion component such as vinyl acetate, acrylic nitrile, acrylamide, styrene, methacrylate, methylacrylate, etc., and a monomer having functional groups for improving adhesive strength and for initiating cross-linking, methacrylic acid, acrylic acid, itaconic acid, hydroxyethyl methacrylate, hydroxypropyl methacrylate, dimethylaminoethyl methacrylate, dimethylaminomethyl methacrylate, acrylamide, methylolacrylamide, glycidyl methacrylate, maleic anhydride, etc., can be preferably employed. The Tg (the glass transition point) of the copolymer is preferably xe2x88x9255 to xe2x88x9215xc2x0 C., and is more preferably xe2x88x9255 to xe2x88x9230xc2x0 C. The weight average molecular weight thereof is preferably 250,000 or more, and is more preferably 250,000 to one million.
In the case in which an adhesive layer consists of an adhesive in which the Tg is lower than xe2x88x9255xc2x0 C. and an adhesive in which the weight average molecular weight is below 250,000, the powders once adhered are torn away by the impulsive force of the pressure media since the layer is too soft, and defects such as powder coming off, etc., occur easily. In addition, the adhesive adheres to the powders after they are torn away, and the powders are adhered on the powder layer again. Furthermore, in the case in which the adhesive layer is too soft, the powders are rotated in a longitudinal direction on the surface of the adhesive layer by impact of the pressure media. Whereby, the position, in which the adhesive is adhered, of the powders appears on the surface of the powder layer and other powders are adhered thereto, or the adhesive oozes from openings of the powders by the impulsive force of the pressure media or by capillarity, and other powders are adhered thereto. Since the powder layer is easily formed as a multilayer constitution by such phenomena, a soft adhesive layer is not desirable. In contrast, in the case of an adhesive layer in which the Tg is higher than xe2x88x9230xc2x0 C., this is not desirable since the adhesive strength is insufficient and the powders easily fall off in the process of washing off surplus powders, etc.
In addition, in the above adhesive, as a hardener, specifically, a crosslinking agent of the metal chelate type, isocyanate type, and epoxy type can be employed alone or in combination, as necessary. It is desirable in practice that the hardener be mixed so that adhesive strength (Japanese Industrial Standard Z-02378) of the adhesive layer is 100 g/25 mm or more. In the case in which the adhesive strength is below 100 g/25 mm, falling off of the powder occurs and environmental resistance is deteriorated. In particular, there is a risk that the adhesive layer will come off the base material under high-temperatures and high-humidity. In addition, from the viewpoint of reliability, the gel fraction after hardening is preferably 40% or more, is more preferably 50% or more, and is most preferably 60% or more. In the case in which the gel fraction is below 40%, there is a risk that the adhesive layer will soften under high-temperatures and high-humidity, the powders will sink in the adhesive layer, and properties of the powder film will change. Furthermore, a UV curable-type adhesive added to the photopolymerizing monomer, oligomer, polymer and photopolymerization initiator may be employed in the adhesive. In addition, various additives such as coupling agents, surface tension adjusting agents, color pigments, dyes, waxes, thickeners, antioxidants, rust-preventive agents, antibacterial agents, ultraviolet absorbing agents, etc., may be added to the adhesive as necessary.
An acrylic type adhesive is coated on one side or both sides of the above base material directly or via another layer by a coating method such as air doctor coating, blade coating, knife coating, reverse coating, transfer roll coating, photogravure roll coating, kiss coating, cast coating, spray coating, slot orifice coating, calender coating, electrodeposition coating, dip coatings, die coating, etc., or a printing method such as letterpress printing such as flexography, etc., intaglio printing such as direct gravure, offset gravure, etc., lithographic printing such as offset printing, etc., stencil printing such as screen printing, etc., or the like, and this is laminated as an adhesive layer. In particular, a coating using a roll coater is desirable, because a uniform layer thickness is obtained. Although the thickness of the adhesive layer is not particularly limited, it is preferably about 0.1 to 5 times the volume average particle diameter of powders to be embedded, since the adhesive layer is wasted when it is too thick.
In the case in which the hardener component is included in the adhesive layer, it is preferable that the adhesive layer be protected by a separation PET film, etc.; it is aged at about 20 to 80xc2x0 C. for about 3 to 14 days; hardness of the adhesive layer be stabilized by sufficiently reacting the adhesive and the hardener at the cross-linking point of the adhesive; and then the next process be carried out.
Process 2: Adhesion of Powder to the Surface of Adhesive Layer
Next, by carrying out a process in which powders are previously adhered on the surface of an adhesive layer on a base material, pressure media can be prevented from adhering to an adhesive layer, and in addition, the powder layer can be formed so that the filling density in the planar direction is high and is uniform.
A film obtained by a forming method of the present invention refers to a film formed in order to give various functions such as polishing application, non-slipping or slipping application, light-reflecting or anti-reflecting improvement application, insulating application, heat radiation application, endothermic application, etc., on a surface of a base materials, and this is broadly applicable in the present invention.
Powders which can be used in each application are illustrated in the following.
(a) Imparting Grinding, Polishing, and Brushing Functions:
In this case, coated objects serve as files or abrasives.
Examples of powders to be used: atomized kelmet powder, bronze powder, sodium montmorillonite powder, zircon sand powder, alumina powder, silicon carbide powder, cerium powder, glass powder, diamond powder, boron carbide powder, aluminum nitride powder, silicon nitride powder, etc.
(b) Imparting Non-Slip Function
Examples of powders to be used: atomized kelmet powder, bronze powder, sodium montmorillonite powder, zircon sand powder, alumina powder, silicon carbide powder, cerium powder, glass powder, etc.
(c) Imparting Slippage (Decreasing Wear) Function
Examples of powders to be used: graphite powder, resin powders such as polytetrafluoroethylene, nylon, polyvinylidene fluoride, fluoroethylene-propylene copolymer resin, etc., or the like
(d) Imparting Light Reflection, Diffusion Function
In this case, coated objects serve as reflection marks, reflection sheets, reflection crosses, LCDs, ELs, FEDs, etc.
Examples of powders to be used: glass powder, inorganic-type powders such as silica, alumina, etc., organic-type powders such as acrylic resin, polystyrene resin, polyethylene resin, epoxy resin, silicone resin, polyvinylidene fluoride, Teflon, etc.
(e) Imparting Light Reflection Prevention Function
Examples of powders to be used: silica powder, titania powder, etc.
(f) Imparting Electrification
Examples of powders to be used: resin powders such as nylon, polyethylene, methacrylic resin, polytetrafluoroethylene, fluoroethylene-propylene copolymer resin, etc. or the like
(g) Imparting Conductivity, Non-Electrification
Examples of powders to be used: aluminum powder, zinc powder, copper powder, gold powder, silver powder, nickel powder, iron powder, tungsten powder, carbon black powder, etc.
(h) Imparting Electric Insulation
Examples of powders to be used: chrysotile powder, silicon carbide powder, etc.
(i) Imparting Heat Radiation
Examples of powders to be used: molybdenum powder, tantalum powder, etc.
(j) Imparting Anticorrosiveness, Heat-Resistance
Examples of powders to be used: niobium powder, tantalum powder, kaolinite powder, kaolin powder, halloysite powder, pottery stone powder, agalmatolite powder, sericite powder, allophane powder, sizicon sand powder, alumina powder, glass powder, etc.
(k) Use as Polarizer
Examples of powders to be used: ferromagnetic particles such as iron, iron oxide, chromium oxide, etc., or the like
(l) Imparting Heat dissipation, Endothermy
Examples of powders to be used: copper powder, magnesia powder, etc.
In the case of use of the above powders, since by uniformly transmitting impulsive force of granular pressure media to powders, the filling density in the planar direction of a powder layer can be increased and be made uniform, and in addition, the embedding depth of the powders in an adhesive layer can be made uniform. Therefore, it is preferable that the powders satisfy the following conditions.
{circle around (1)} It is desirable that particle size distribution of the powders be sharp, and specifically, it is preferably 0.8 to 1.0, and is more preferably 0.9 to 1.0.
{circle around (2)} It is desirable that powders be globular and that the roundness of the powder is preferably 80% or more and is more preferably 90% or more.
In the present specification, the volume average particle diameter of powders is defined by the following general equation (1), and the particle size distribution of the powders is defined by the following general equation (2).
Particle size distribution=Number average particle diameter/Volume average particle diameter.xe2x80x83xe2x80x83(1)
Number average particle diameter=An average value in which diameters of 100 powders sampled at random are measured and are averaged
xe2x80x83Volume average particle diameter=A diameter of powder in which powder particles are regarded as being true spheres; each volume is calculated by diameters of 100 powders sampled at random; and the volumes are added up in order of small volume until the added value is reached to 50% of the total volume summed up all calculated volumes.xe2x80x83xe2x80x83(2)
In addition, xe2x80x9croundnessxe2x80x9d is defined by the following general equation (3).
Roundness (%)=(4xcfx80A/B2)xc3x97100xe2x80x83xe2x80x83(3)
A: Projected area of powder
B: Circumference of powder
For example, projection images are obtained by photographing using a transmission electron microscope, and are subjected to an image analysis using an image analysis apparatus (for example, trade name: EXECL II; produced by Nippon Avionics Co., Ltd.), and the above A and B are thereby obtained. Subsequently, roundness can be calculated from the A and B. As is apparent from the above equation (3), the closer the powder approximates a true sphere, the closer the roundness approximates 100%, and in the case of an undefined shape, the roundness is less than that value. In the present specification, average value measured with respect to 10 powders is defined as roundness.
As a specific method for adhering the above powder to the surface of the above-mentioned adhesive layer, for example, a method in which powders filled in a container are fluidized by vibration or fluidization air and a base material is passed under this fluidized powder, and a method in which powders are sprayed on the adhesive layer by air spraying, can be employed. At this time, with respect to a powder in which the particle size distribution is 0.8 to 1.0 or in which roundness is 80% or more, the powders are easily fluidized in the container since the specific surface is small and fluidity is high, and in addition, the powders are easily mixed with air in the case of air spraying. Therefore, such powder is suitable for uniformly adhering to the surface of the adhesive layer. In a process for embedding the powders in the adhesive layer by pressure media, by uniformly adhering the powders to the surface of the adhesive layer, the pressure media can be prevented from adhering to the adhesive layer and defects such as powder coming off can be also reduced. In this process, it is sufficient if only the powders are adhered to the surface of the adhesive layer by adhesive strength of the adhesive layer, and there is no problem even if the powders are adhered so as to form multiple layers.
Process 3: Embedding Powders in Adhesive Layer
Powders adhered to the surface of the adhesive layer are embedded in the adhesive layer by impulsive force of pressure media. As such a method, pressure media are put into a suitable container and are vibrated with the container, a base material in which powders are adhered to the surface of an adhesive layer is put into this vibrated pressure media or is passed under this vibrated pressure media, and impulsive force is thereby imparted to the powders. Thus, the powders are struck by the pressure media and are thereby embedded in the surface of the adhesive layer. The granular pressure media is characterized in that the powders can be embedded in the adhesive layer to a uniform embedding depth because the granular pressure media can be uniformly struck over a small area of the powders. That is, filling density in the planar direction of the powder layer can be increased and be made uniform, since other powders can be pushed into openings between the powders adhered on the surface of the adhesive layer in the above process to a uniform depth by impulsive force of the pressure media. According to such a method, powders are formed as a powder layer in which the powders are uniformly embedded in the adhesive layer at high density, as a monolayer, without the powders piling up in the adhesive layer, so that embedding depths are made uniform and part of the powder protrudes from the adhesive layer. At this time, in order to make up for a shortage in the amount of powder, pressure medium previously mixed with about 0.5 to 2.0 parts by weight of powder to 100 parts by weight of pressure medium may be used.
As an external force for embedding powders, in addition to vibration, rotation, falling, etc., may be adopted. In the case of rotation, a rotating container, a container having stirring fins therein, etc., can be used. In the case in which falling is adopted as an external force, a V blender, a tumbler, etc., can be used.
Hereinbelow, pressure media for embedding powders are explained. The pressure media are particles to cause powders to be embedded in an adhesive layer by striking due to vibration, etc., as described above. As a pressure medium, particles consisting of iron, carbon steel, alloy steel, copper and copper alloy, aluminum and aluminum alloy, and other various metals or alloys; particles consisting of ceramics such as Al2O3, SiO2, TiO2, ZrO2, SiC, etc.; and in addition, particles consisting of glass, hard plastics, etc.; can be used. Furthermore, particles consisting of hard rubber may be used if a sufficient stroke force can be imparted to the powders. In any case, material for the pressure medium is chosen appropriately depending on the material of the powder, etc. In addition, it is desirable that the shape thereof approximate a true sphere so that pressuring force is made uniform when applied to the powders, and it is desirable that total particle distribution be as narrow as possible. The particle size of the pressure medium is chosen appropriately depending on material and embedding depth of the powder, and in particular, it is preferably about 0.3 to 2.0 mm.
Process 4: Removing Surplus Powders
After the embedding process of the powders in the adhesive layer, surplus powders are removed. Surplus powders are, for example, powders which are embedded imperfectly in the adhesive layer, or which only adhered on embedded powders by interparticle forces such as electrostatic forces, van der Waals forces, etc. Such surplus powders can be removed by washing in water or by applying fluidic pressure by air blasts, etc., to the powder layer. At this time, in the case in which the particle size of the powder is relatively small, it is desirable that the powder layer be washed wet using ion exchanged water, etc. In addition, in the case in which the volume average particle diameter is 15 xcexcm or less, it is preferable that the powder layer be soaked in ion exchanged water to which is added a washing auxiliary agent such as a surfactant, etc., or the like, and be subjected to ultrasonic washing, etc., and then be rinsed sufficiently by deionized water, etc., and be dried, since there is a risk that the surplus powder will be insufficiently removed by use of fluidic pressure alone.
Secondly, a production method for a filler lens according to second embodiment of the present invention is explained. In the production method, only differences are explained since it is almost the same as in the first embodiment, and subsequently, compositional materials which are suitable for filler lens produced by the present embodiment are explained.
(1) Production Method
In the coating process of the adhesive layer, the thickness of the adhesive layer is preferably 0.5 to 2 times the average particle diameter of the embedding filler.
In the embedding process of fillers, in order to prevent fillers from coming out from the adhesive layer and to reliably yield a lens effect by protruding the fillers from the surface of the adhesive layer, the embedding depth of fillers is preferably such that the fillers are embedded in the adhesive layer to a depth of 10 to 90% of the diameter, more preferably 30 to 90%, and most preferably 40 to 70%, and this can be adjusted depending on the optical properties of the lenses.
In the present embodiment, a process for curing the adhesive layer is included between the embedding process for fillers and the removing process for surplus fillers. In this process, an adhesive is cured by exposure to radiation such as ultraviolet light, electron beams, etc., of the adhesive layer embedded fillers. Until the above embedding process of fillers, it is desirable that the adhesive be soft and that the embedding depth of fillers be easily controlled, and after the fillers are embedded, in order to maintain optical properties of the filler lens, it must be radiation-cured so as not to be susceptible to flowing under high-temperatures and high-humidity.
The adhering process of fillers and the removing process of surplus fillers are the same as that of the first embodiment.
(2) Compositional Materials
{circle around (1)} Base Material
As a base material for the filler lens of the present embodiment, well-known film shaped materials or sheet shaped materials, specifically, base materials consisting of material described in the above first embodiment, can be employed. Non-transparent base materials can be also employed even if light can penetrate therein, and in particular, in the case in which it is used in a liquid crystal display, etc., it is preferable that transparent base materials have a refractive index (Japanese Industrial Standard K-7142) of 1.45 to 1.55, in order to adapt the refractive index therefor. As such a transparent base material, acrylic resin film such as triacetylcellulose (TAC), polymethyl methacrylate, etc., can be employed. The higher the transparency thereof, the more desirable the transparent substrate. The light transmittance (Japanese Industrial Standard C-6714) is preferably 80% or more, and is more preferably 90% or more. The Haze value (Japanese Industrial Standard K-7105) is preferably 1.0 or less, and is more preferably 0.5 or less. In the case in which the transparent base material is used for a small and lightweight liquid crystal display, it is more preferable that the transparent base material be of a film shape. The thickness of the base material is desirably thin from the viewpoint of illumination as in the first embodiment, and it is preferably 1 xcexcm to 5 mm in consideration of productivity.
{circle around (2)} Adhesive Layer
The adhesive layer in the present embodiment contains at least radiation (ultraviolet ray, electron beam, etc.) curable resin. In such a resin, hardeners such as crosslinking agents, polymerization initiators, etc., polymerization promotors, solvents, viscosity modifiers, etc., can be added as necessary, and can be used alone or in combination. In the case in which the base material is a plastic film, the curing temperature cannot be set high. In particular, in the case in which PET or TAC is used, it is desirable that the curable resin can be cured at 100xc2x0 C. or less.
As a radiation curable type resin, specifically, polyester resin, polyether resin, acrylic resin, epoxy resin, alkyd resin, polybutadiene resin, spirol acetal resin, urethane resin, oligomers or prepolymers of (metha)acrylate as a multifunctional compound such as the polyalcohol, can be employed. As a reactive diluent, monofunctional monomers or polyfunctional monomers such as ethyl (metha)acrylate, ethylhexyl (metha)acrylate, styrene, methylstyrene, N-vinylpyrrolidone, etc., or the like, can be employed. In particular, acrylic resin is preferred, since transparency, water resistance, heat-resistance, light resistance, adhesive strength, etc., are superior, and in addition, the refractive index is easily adjusted so as to adapt therefor in the case in which it is used in a liquid crystal display.
In the adhesive layer, a thermosetting resin can be employed, in order to adjust the adhesive strength, etc. As a thermosetting resin, acrylic resin, phenol resin, melamine resin, polyurethane resin, urea resin, diallylphthalate resin, guanamine resin, unsaturated polyester resin, amino alkyd resin, melamine-urea cocondensated resin, silicon resin, polysiloxane resin, etc., can be employed. Of these resins, acrylic resin is particularly preferred because of adhesive strength, viscosity control of coating material, transparency, etc. As an acrylic type adhesive, specifically, a homopolymer or copolymer of an acrylic monomer such as acrylic acid and esters thereof, methacrylic acid and esters thereof, acrylamide, acrylic nitrile, etc., and copolymers of at least one kind of the above acrylic monomers and aromatic vinyl monomer such as vinyl acetate, maleic anhydride, styrene, etc., can be employed. In particular, copolymers consisting of primary monomers for providing adhesiveness, such as ethylene acrylate, butylacrylate, 2-ethylhexyl acrylate, etc., monomers as a cohesion component, such as vinyl acetate, acrylic nitrile, acrylamide, styrene, methacrylate, methylacrylate, etc., and monomers having functional groups for improving adhesive strength and for cross-linking initiation, methacrylic acid, acrylic acid, itaconic acid, hydroxyethyl methacrylate, hydroxypropyl methacrylate, dimethylaminoethyl methacrylate, dimethylaminomethyl methacrylate, acrylamide, methylolacrylamide, glycidyl methacrylate, maleic anhydride, etc., can preferably be employed. The Tg (glass transition point) of the copolymer is preferably xe2x88x9260 to xe2x88x9215xc2x0 C., and the weight average molecular weight thereof is preferably 200,000 to 1,000,000. When the Tg is below xe2x88x9260xc2x0 C., the adhesive layer is too soft and an embedded filler layer is easily damaged. In contrast, when the Tg is above xe2x88x9215xc2x0 C., it is difficult to embed fillers.
In order to cure radiation curable type resins used in the present embodiment, for example, although radiation such as ultraviolet light, electron beams, X-rays, etc., may be irradiated, it is necessary to add a photopolymerization initiator when it is to be cured by ultraviolet light. As a photopolymerization initiator, benzophenones, xcex1-amyloxim ester, Michler""s benzoyl benzoate, tetramethylthiuram monosulfide, thioxanthones, can be employed by mixing therewith, and as a photo sensitizer, n-butylamine, triethylamine, etc., can be also employed. The content of the photopolymerization initiator is preferably 0.1 to 10% by weight to the radiation curable type resin. The effect is deteriorated above or below this range. As a hardener for the thermosetting resin, for example, crosslinking agents of the metal chelate type, isocyanate type, or epoxy type, can be employed alone or in combination, as necessary.
In the present embodiment, it is desirable in practice that adhesive be mixed in the adhesive layer so that adhesive strength (180 degree pulling out adhesive strength according to Japanese Industrial Standard Z-0237) of the adhesive layer before curing the radiation curable type resin is 50 to 3000 g/25 mm, and the adhesive strength after radiation curing is 30 g/25 mm or less. In the case in which adhesive strength before curing is below 50 g/25 mm, it is difficult to embed fillers, and embedded fillers easily fall out. In contrast, in the case in which it is above 3000 g/25 mm, fillers are excessively embedded and the surface of the formed filler layer is easily damaged and yields easily to pressure. Furthermore, in the case in which adhesive strength after curing is above 30 g/25 mm, the surface of the filler layer is easily damaged and yields easily to pressure, environment resistance is deteriorated, and in particular, there is a risk that optical properties will change under high-temperatures and high-humidity.
{circle around (3)} Filler
As a filler, transparent or white pigment of an inorganic type such as silica, alumina, etc., transparent or white pigment of an organic type such as acrylic resin, polystyrene resin, polyethylene resin, epoxy resin, silicone resin, polyvinylidene fluoride, Teflon, etc., or the like, can be employed. In particular, silica, acryl beads, and silicon beads are preferred. The filler is preferably globular and the roundness is preferably 80% or more, and is more preferably 90% or more. A globular filler has a merit in that dispersion of the embedding depth is difficult to cause. Average particle diameter (Japanese Industrial Standard B-9921) is preferably 1 to 50 xcexcm, is more preferably 3 to 30 xcexcm, and is most preferably 3 to 9 xcexcm. In addition, in order to yield a good lens effect, it is preferable that the particle size distribution be narrow, and in the case of mono-dispersion, the best effect is obtained. Here, xe2x80x9croundnessxe2x80x9d in the present embodiment is the same as defined in the above first embodiment.
In the case in which it is used in a liquid crystal display, etc., it is preferable that the refractive index of the filler be 1.45 to 1.55, in order to adapt the refractive index therefor, and in addition, each difference in refractive index between a base material, an adhesive layer, and a filler are preferably below 0.30, and are more preferably below 0.15.
{circle around (4)} Other Layers
As another layer, an adjustment layer for adjusting the refractive index or permeability of the light, binding layer for firmly binding a base material and an adhesive layer, etc., may be provided.